This invention relates to a master cylinder for a vehicular brake and more particularly, to a tandem-type master cylinder for a vehicular brake.
There have been proposed and pratically employed a great variety of tandem-type master cylinders for vehicular brakes and in one of the prior art master cylinders of such type, in order to make the pressure produced by the front piston equal to that produced by the rear piston within the cylinder, an equalization cylinder is movably disposed between the pressure generation chambers associated with the two pistons to adjust the pressures within the chambers so as to equalize the pressures. However, such an equalization cylinder is adapted to move in opposite directions within the cylinder and such movement of the equalization cylinder is an oscillatory movement and is not rapid and precise. And since the equalization cylinder is adapted to move back and forth within the cylinder, the equalization cylinder should be maintained in its neutral position before the equalization cylinder is operated. Therefore, the number of parts of the master cylinder is increased and as a result, the overall length of the master cylinder becomes undesirably long.
In most of the other prior art master cylinders, as the piston advances within the cylinder, the primary cup seal provided in a front portion of the piston serves as a seal means which closes the relief port to pressurize the liquid within the pressure chamber and forces the liquid under pressure to be discharged into the brake system and the oil replenishment chamber is provided in the piston itself. In such an arrangement of the prior art master cylinder, as the piston retracts within the cylinder, the primary cup seal serves to release the oil from the oil replenishment chamber into the pressure chamber. More particularly, in such prior master cylinders, as the piston moves back and forth within the cylinder, the cup seal on the piston alternately expands and shrinks. Thus, the cup seal should be designed to have a rigidity sufficient not to be damaged when the seal passes by the relief port in its advance movement and also a flexibility sufficient to readily flex to open the relief port as the cup seal moves away from the relief port in its retraction movement. However, in designing the cup seal practically, it is impossible to perfectly meet these requirements.
Furthermore, as mentioned hereinabove, in the prior art master cylinders, since the oil replenishment chamber is provided in a reduced diameter rear portion of the piston rearwardly of the primary cup seal, the length of the piston is increased by the amount corresponding to the length of the oil replenishment chamber which is a serious obstacle in reducing the length of the overall length of the cylinder.